Nguyen, a Vietnamese developer with a studio called DotGears, did not reply to CNN’s request for an interview last week and has stayed mostly quiet in the wake of the game’s recent and sudden success.

His no-frills game gave players a chance to steer a tiny bird through an obstacle course of metal pipes. But it’s unclear why it shot to the top of the most downloaded charts.

It was originally released for the iPhone in May but didn’t become the top free iPhone app until mid-January, following a surge in popularity that seems to have kicked off in early December.

Nguyen told Chocolate Lab Apps he created the game in two to three days and says he did not promote the app in any way after its release.

In a series of Twitter posts Saturday, he said he wouldn’t sell “Flappy Bird” and would continue to make games.

“It is not anything related to legal issues,” he said. “I just cannot keep it anymore.”

There were some unproven theories floating around about the game’s success, including the use of bots to get it on Top 10 lists artificially, organic enthusiasm on social media and a surge in amusing user reviews in the Apple App and Google Play stores. Last week, “Flappy Bird” had an average four-star rating from more than 543,000 reviews in the Apple App Store and 228,000 on Android.

Many of the reviews were lengthy, tongue-in-cheek tales of time lost, marriages ended and people going cuckoo after playing the game.